The aim is to understand development of the sound system by children with functional (nonorganic) phonological delays. Six projects are planned to evaluate the way in which children restructure their representation of words in the mental lexicon. Each project utilizes single-subject experimental clinical treatment to induce restructuring of the sound system. The hypotheses are that phonological restructuring will be influenced by the way in which children's representations are initially structured, organized and accessed from the lexicon. These hypotheses derive from contemporary linguistic and psycholinguistic models to potentially contribute to an integrated view of language and language processing. The outcome of this research holds clinical application in the design, implementation and efficacy of treatment for children with functional phonological delays.